Guiding Options

GNIRS can be used with the standard Gemini peripheral wavefront
sensors, or with the Altair adaptive optics module in both natural and laser guide star modes. The Altair web pages give details of guide star limiting magnitudes etc.

The peripheral wavefront
sensors (PWFS) operate in the optical. Hardware changes to PWFS1 in late 2011 mean that PWFS1 and PFWS2 are now roughly equivalent, although PWFS1 has a slightly larger vignetting footprint. The PWFS can be used down to ~4.7' from the science target. In XD mode, or if some vignetting of the slit and/or acquisition field of view can be tolerated, guide stars closer to the science target can be used (check
for vignetting in the OT Position Editor and please add a note alerting
the observer). The outer radius for PWFS guide stars can be displayed on the OT position editor and is discussed here. Always check the guide stars "auto-selected" by the Phase I
tool, as the guide star catalogs have many spurious entries. Extended
objects and binaries should be rejected.

There is also an on-instrument wavefront sensor with a
HgCdTe detector to allow guiding on near-infrared bright stars. The OIWFS could in principle be used in several modes, but is most likely to be useful for correcting flexure between GNIRS and Altair or the PWFS. The OIWFS has not yet been commissioned.